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The science of cooking with olive oil

Submitted by TomOct 10 2013

Mary Flynn, PhD, RD, is Associate Professor of Clinical Medicine at Brown University’s Alpert Medical School in Providence, Rhode Island. In her first contribution to Truth in Olive Oil, she covered some basic facts of olive oil health, and explained how she came to know, and then love, extra virgin olive oil for its health and nutritional properties. Here she shares some vital advice about cooking with extra virgin olive oil, based on her several decades of oil-related research and clinical trials. She also explodes some common olive oil myths, including the bizarre but persistent "don't cook with extra virgin olive oil" fallacy, and offers 3 of her olive oil-based recipes. Each month, Mary will donate another recipe to Truth in Olive Oil.

Eating and cooking with olive oil

I started to develop my plant-based olive oil diet in 2000, primarily including foods that would improve health and control weight. I saw extra virgin olive oil as a central part of this diet for several reasons. I knew it would improve health, but I also thought that using olive oil might increase vegetable intake – another key to good health – since it makes vegetables taste so much better. Also, I believed that using olive oil at meals would help people to eat less, because including fat in a meal makes the meal more satisfying and delays the onset of hunger after the meal. All fats do this, but olive oil is the best choice because it's a very healthy fat.

Extra virgin olive oil is the juice of the olive fruit. Like most unprocessed plant products, it contains a range of health-promoting phytonutrients. The phytonutrients in olive oil have been shown to decrease the oxidation of LDL (1) (which would lower heart disease risk) and DNA (2) (which would lower cancer risk). Other phytonutrients in olive oil have been shown to decrease blood levels of glucose and insulin (3); decrease blood pressure (4, 5); decrease blood coagulation (6); and decrease inflammation (7). This makes extra virgin olive oil very different from seed oils, like soybean, safflower, corn, and canola oil, which have undergone a refining process that destroys phytonutrients. Refined olive oil, typically labeled “olive oil” in stores, also lacks phytonutrients. (Take-away point: buy only extra virgin olive oil!)

I recommend the use of at least 3 tablespoons (45 ml) of extra virgin olive oil per day, most of which you’ll use to cook vegetables. In the studies cited previously, the health benefits of extra virgin olive oil consumption started at about 2 tablespoons a day, so using 3 tablespoons will ensure that you get these health benefits, and will likely increase your vegetable intake as well. The use of olive oil to prepare vegetables greatly improves the taste of vegetables, particularly those that are naturally bitter, like many leafy greens, or those that contain sulfur (the brassica family – broccoli, Brussel sprouts, cabbage, cauliflower, kale). I recommend 1 tablespoon of olive oil per cup of vegetables. In addition, brassica vegetables contain a phytonutrient family (glucosinolate) that has been shown to be cancer protective (8), but it is water soluble (9), so boiling or steaming these vegetables means you will not get the health benefits from this phytonutrient, since it will be lost in the cooking water. Cooking the brassica family in extra virgin olive oil therefore means that you get both the health benefits of olive oil itself and of the cancer-fighting phytonutrients in the vegetables. Plus using olive oil will make them taste so much better than boiling or steaming!

In the 12 years that I’ve employ my diet in my work, I have found, just as I’d hoped, that when my patients and study participants use more olive oil, they consume more vegetables (10, 11), a big plus for health. In addition, when they report using more than 3 tablespoons of olive oil a day – for example when summer vegetables are plentiful – they are still losing weight. I would guess there is some upper limit to how much you extra virgin olive oil you can consume before you start gaining weight, but I haven’t yet found it. In fact, I tell patients that they can never eat too much extra virgin olive oil. Sure, it’s a fat, but the benefits of extra virgin olive oil clearly outweigh its drawbacks – olive oil will improve your health.

Olive oil and vegetables

Vegetables, like olive oil, have long been associated with improved health. However, studies looking at the consumption of vegetables do not consistently show decreases in chronic diseases. There are at least as many studies showing no benefit as those indicating some disease protection from frequent consumption of vegetables. I believe this inconsistency may be attributable to the type of vegetable consumed in the studies, and to the way the vegetables are prepared. Certain plant products are clearly more health-protective than others, due to the phytonutrients they contain. Some of the healthiest, vegetables, which I recommend to my patients, include: all the brassica family – broccoli, Brussel sprouts, cabbage, cauliflower, kale; any vegetable with deep color, like carrots, peppers, winter squash; and anything leafy and green – spinach, collard greens, etc. I also recommend the use of frozen vegetables; in fact, I prefer them nutritionally over fresh as in many cases they are kept on the plant longer than what one would buy in a grocery store, so their phytonutrient is likely higher and they have the same vitamin content as store-bought fresh vegetables (12, 13). (I’ll write more on vegetables and health in an upcoming post.)

Low cost of meals that contain olive oil

I think it’s wrong, when considering the cost of olive oil, to consider it as another vegetable oil and compare its cost to theirs. Vegetables oils are chemically extracted from seeds and nuts and do not have health benefits remotely comparable to extra virgin olive oil, which is physically extracted from a fruit – the olive. If properly made, extra virgin olive oil is rich in many components that research has shown to produce manifold health benefits, and to be associated with a lower rate of chronic diseases. What’s more, many vegetable oils are high in polyunsaturated fats, which readily oxidize. I think a case could be made that vegetable oil consumption may actually increase your risk of chronic diseases.

Apart from the considerable health benefits of extra virgin olive oil, when you work out the cost of olive oil per tablespoon, it's actually quite inexpensive. A 17 fl. oz bottle of olive oil contains approximately 32 tablespoons, and a liter contains 64 tablespoons. Many extra virgin olive oils cost less than 30 cents per tablespoon, so my recommended dose of 3 tablespoons of oil per meal costs 90 cents. A health-promoting meal with plenty of olive oil therefore costs substantially less than one with meat, poultry or seafood – foods which in any case won’t improve your health.

“Raising the Bar on Nutrition” (RTB) is a program I developed for the Rhode Island Community Food Bank, after participants in my early research into my plant-based olive oil diet observed how inexpensive my diet was to follow. The recipes for RTB are based on my diet, but use foods commonly found in most food pantries, which are locations where low-income people can get free food. The average cost of my RTB recipes is $1.07 per serving (December 2011 pricing in Rhode Island), and all recipes include 1 to 2 tablespoons of olive oil per serving. RTB was tested as a research protocol using a 6-week cooking program for food pantry clients. Participants in the program had significant decreases in food insecurity, food costs, and body weight (10).

Canola oil is not a substitute for olive oil

Speaking of vegetable oils, I’m often asked about canola. U.S. health officials originally linked the health benefits of olive oil to its monounsaturated fat content, but since they didn’t think Americans would accept a dietary oil with pronounced flavor, like olive oil has, researchers at the University of Manitoba, Canada developed canola oil, which was naturally bred from the rapeseed plant (“canola” stands for “Canadian oil, low acid”). Canola oil is higher in monounsaturated fat than other seed oils, though not as high as olive oil, so the health benefits related to its lipid profile will be less than olive oil. Additionally, canola lacks numerous components contained in extra virgin olive oil which, as we’ve mentioned above, are linked to a range of health benefits. In fact, there are no studies showing health benefits from using canola oil. Bottles of canola oil often say “contains omega 3 fats”, which is true, but not the form of omega 3 that is known to improve health. Canola oil contains an 18-carbon form of omega 3, while health benefits have only been demonstrated with 20- and 22-carbon omega 3s. Humans convert only small amounts of the 18-carbon to the 20 carbon omega 3 compound (EPA) and even less to the 22- carbon compound (DHA) (14, 15), so the health claims concerning canola oil’s omega 3s may be misleading.

Olive oil and cooking

Nearly every time I lecture on olive oil, people ask whether heat destroys the oil, and whether they can cook with it. I don’t know who invented this misconception (seed-oil companies?), but I’d love to dispel it once and for all. High quality extra virgin olive oil can be heated to 420°F before it reaches smoke-point (ie begins to smoke and starts to form unhealthy compounds), which is higher than nearly every other vegetable oil. Olive oil is much more stable when heated compared to most vegetable oil (16, 17). Cooking with olive oil below the smoke-point does not destroy most of its health benefits, or make it less healthy – under normal cooking conditions, most of the therapeutic minor components are retained (18-20). Some studies have subjected olive oil to high temperatures (180°C/356°F) for long periods of time (from 90 minutes to over 20 hours). These conditions do tend to decrease the content of some phytonutrients, yet even under such extreme conditions, some phytonutrients remain (21).

This said, it is true that heating olive oil can modify or impair some of the flavor. So at least from a culinary point of view, and depending on your personal taste, it’s usually better to add high-quality olive oils to finish a dish, after cooking.

I’m also frequently asked if heating olive oil produces trans fats. Here again, the answer is No. Trans fats are created in an industrial process that adds hydrogens to the liquid oil (partial hydrogenation), making it semi-solid. This is how margarine is made (or at least was made, before trans fat were recognized as a health issue). Ordinary cooking, even at high heat, never produces trans fats.

Milder extra virgin olive oil is excellent in baking, especially since heating seems to decrease the bitter taste in some olive oils (20). I tell people to use an extra virgin oil like California Olive Ranch, which is relatively delicate in flavor, as well as economical. (A useful book on choosing different olive oils is The flavors of olive oil. A tasting guide and cookbook by Deborah Krasner (Simon and Schuster, New York 2002), which classifies oils according to taste - delicate and mild, fruity and fragrant, leafy and grassy, peppery - and also lists some oils by country of origin.) The oil gives muffins, quick breads, and even cookies an excellent texture, without any noticeable olive flavor. In fact, many of my patients tell me that my olive oil-based recipes for muffins and quick breads have a better texture than other recipes they've used which call for vegetable oil or margarine. In short, you can use extra virgin olive oil in any recipe that calls for liquid oil.

Preheat the oven to 375°F.
Heat the olive oil on medium in a medium pan. Add the dried red pepper, then the onion and celery. Season with salt. Cook for 5 minutes.
Add the peppers, eggplant and zucchini. Cook for 5 minutes or until some of the oil is absorbed into the vegetables.
Add the tomato and bay leaf. Cook until the vegetables are bubbling (about 5 to 7 minutes).
Stir in the chickpeas and put the mixture in a casserole dish that holds the mixture in layer about 2 ½ to 3 inches deep.
Bake for 30 minutes. Remove from the oven; sprinkle the cheese over the top. Return to the oven and cook another 5 minutes or until the cheese melts.
Serve over the cooked rice.

Serves 1
Calories: 630

Pumpkin Bread

This Pumpkin Bread is moist and flavorful—the perfect answer to a healthy breakfast especially for those who are used to eating high-calorie, negligible-nutrient muffins in the morning. Although the bread has some vegetable (the pumpkin), some fruit (raisins) and olive oil, it does not contain enough of any of them to include in the food count, so count the starch and consider the calories. You can cut the baked loaf into serving-size slices and freeze them individually. The slices will defrost quickly.

Special Equipment:
One 5 x 9-inch loaf pan, preferably non-stick or unglazed, ceramic stoneware. The stoneware gives the bread a particularly nice crust. If neither is available, brush the sides of the pan with olive oil so the bread will release easily.

Preheat the oven to 350°F.
Measure the flour, salt, brown sugar and baking soda into a mixing bowl and stir with a fork to blend the ingredients together thoroughly. Be sure to break up any lumps in the brown sugar.
In a separate bowl, stir the remaining ingredients together until thoroughly blended. Gently stir the mixed dry ingredients into the pumpkin mixture just until combined. A plastic spatula works best. Do not over mix or the bread will not rise.
Pour into a loaf pan and bake 50 to 60 minutes or until a toothpick or cake tester inserted into the center comes out clean. Let the bread cool in the pan slightly, five or ten minutes, then turn it out onto a wire rack and cool thoroughly.

Makes 8 slices
Calories: 370

Broccoli Wrap with Cheese

Can use other vegetables; can use other bread types; wraps tend to not absorb the olive oil but can pack in separate containers; this can also be made by roasting the broccoli for about 20 to 25 minutes in a 450F oven.

Heat the olive oil in a small skillet on medium. Stir in the broccoli. Season with salt. Reduce the heat to medium low and cook for 10 to 15 minutes or until the broccoli is softened.
Sprinkle the cheese over the cooked vegetables and allow the cheese to melt (2 to 3 minutes).
Place the wrap on a plate if eating now or on aluminum foil if packing to eat later. Use a rubber spatula to spread the cooked broccoli and cheese into a circle in the center of the wrap. Fold the bottom of the wrap up over the mixture; fold in the 2 sides. You can secure the wrap with a toothpick, if it is being eaten now. If packing for eating later, wrap tightly in aluminum foil.

Comments

Thank you for this article by Mary Flynn. I've labored under the impression that heating olive oil beyond, say, medium heat was unhealthful. Glad to hear this isn't so. I look forward to more of her thoughts on the oil and more recipes.

I agree with everything you have written. Although my knowledge is mostly self taught I rely on uncommon sense, logic and people like yourself for reliable information. I also realize that PhD's can be just as adulterated as many of the so called Extra Virgin's.

I grew up on the Mediterranean diet which of course included EVOO. Recently however I became caught up in the "olive oil debates" and completely eliminated it for over a year. I am now including it back into our diet and suggesting it's use to my clients again. Thank you for your work and the article with it's many great points. Carol D.

Thanks for sharing such an informative article with recipes with us. I really liked the detailed you mentioned in your post. Olive Oils are also very helpful in maintaining the good health.
I have learnt many new things about Best olive oil from your article.

I just saw your blog posts when I was doing some research on Olive Oils in California. Have you ever tried Capay Valley Ranches Olive Oil? I know the owners (the actual farmer, Chris Steele) and his trees are amazing. They just had a gigantic crop that produced over 12,000 gallons of Arbequina olive oil, that tastes amazing, with that great pepper finish you have with all great, fresh olive oils. Check it out: http://www.cvranches.com/ They are also selling quite a few other styles of Olive oils and Almonds that they grow there, including flavored oils and Balsamics.

Thank you very much for this no-nonsense, research-backed article about olive oil. In particular, I greatly appreciated your paragraph about heating olive oil and the fact that it doesn't become a trans-fat under normal cooking conditions. Too many web sites state the opposite (without research backing their statements) and it's been something I've been worried about until I read your article.

Perhaps you can answer one related question: some of the latest "propaganda" against using olive oil for cooking states that it create acrylamides when heated, and thus can cause cancer and other nasty things. Can you comment about that? I suspect the truth may be only beyond the smoking point (so no issue under normal cooking conditions), but it would sure be nice to hear the scientific facts.

Hi Jean-Marc, I've started hearing this too. My impression is that it's also true of all other vegetable oils (discussions on this topic are cropping up a lot in Eurofed Lipids and other conferences), and above smokepoint. But I will check with an expert and get back to you on this important question.

"Acrylamide does not appear to be in raw foods themselves. It is formed when certain starchy foods are cooked at temperatures above about 250° F. Cooking methods such as frying, baking, broiling, or roasting are more likely to produce acrylamide, while boiling, steaming, and microwaving appear less likely to do so. Cooking at high temperatures causes a chemical reaction between certain sugars and an amino acid (asparagine) in the food, which causes acrylamide to form. Longer cooking times and cooking at higher temperatures can increase the amount of acrylamide in foods further.

Acrylamide is found mainly in foods made from plants, such as potato products, grain products, or coffee. Foods such as French fries and potato chips seem to have the highest levels of acrylamide, but it is also found in breads and other grain products. Acrylamide does not form (or forms at lower levels) in dairy, meat, and fish products."

Hi, great article, thanks! I especially love the comment about the seed oil companies' claims. I have tried to find the answer to this - does pressure cooking of say, rice and beans, generate acrylamides too? Also, so bread isn't all that healthy then? I look forward to your responses.

Thank you Tom for the links you provided regarding studies on acrylamide. There's definitely much quality scientific data out there, but as you pointed out, the jury is still out on olive oil specifically. For the time being, my takeaway from all this is cooking with olive oil probably doesn't create much if any acrylamide, as long as it's below the oil smoke point and as long as we make sure we don't burn the starchy veggies to keep glycation from happening. On the other hand, high heat frying (whether with olive oil or no oil) isn't a good thing since the glycation process or process of burning is what seems to create the acrylamide.

The bottom line is stir frying vegetables at medium heat without burning them seems like a healthy (and tasty) approach. Frankly, that's the conclusion I was hoping for as we love to stir fry our veggies with extra virgin olive oil and fresh garlic. :)

I think it is wonderful how science is proving many of the things that have come to us from the ancient knowledge of indigenous peoples. I thought this was so amazing that these primitive people could instinctively 'know' so much without science! But recently, I've realized (and this has been confirmed by your article) that the very same wisdom lies within me still! Point in case: I have been using evoo for many years, gradually coming to the point of exclusively. Studies and health articles have helped me to make this choice. I also use organic (preferably grass-fed) butter and organic unrefined coconut oil. (Ghee, by the way, or clarified butter, is used in India. The clarification process enables its preservation without refrigeration in those hot climates.) In the case of evoo, I have used it for cooking and without any information to guide me, came to the conclusion that, if it began to smoke before I began to cook in it, it then had a bad smell and taste, so I would throw it out and start over. Most acrylimide formation is associated with deep-frying, so I don't. Also, a friend did an experiment years ago with many various unrefined oils. He put a very small amount of several oils, each kind in individual very small dark brown bottles. He left them for ten years in his cabin in Phoenix, AZ. without heat or any type of cooling. (Actually, he meant to do this for a year, but forgot about them for 10 years!) When he went back to these after all these years and opened each bottle (I was there so I can attest to this) each if these bottles of various oils smelled completely rancid, EXCEPT for the EVOO, which smelled and tasted excellent! Perhaps this is why EVOO became the oil of choice for ancient Mediterranean cultures. (By the way, the other oils he stored away were: sunflower, safflower, sesame, soy, and peanut. The sesame and peanut oils were the only other two that even remotely smelled and tasted at all like themselves. But they were, nevertheless, quite a bit on the rancid side. The other oils were absolutely rancid, unrecognizable in flavor, and nasty to the MAX!) As for the various cooking methods, without any knowledge of nutrient values, I have also learned, by taste, which foods to never steam or boil, as they lose their flavor. This concurs with the authors research. Fresh vs. Frozen vs. Freshly picked and organically grown all have different flavors, if one pays attention. I trust my taste buds! (As do the squirrels offered a choice between GMO corn and organically grown corn. Nobody likes the GMO corn, when given the choice! Hopefully, we will always have a choice, or, preferably, GMOs and all non-organic, non-sustainable farming methods will be outlawed, and our soils be restored, by our consistent and conscientious efforts, for the health of all. By the way, I enjoyed your article. Keep up the good work! I will pass it on.

I really believe that olive oil is better than other oils. I really feel great when I use it in salads. Yet, I get acne and my hair falls like crazy. I have bought several expensive brands: organic, overseas, and they all give me the same problem. I wonder if someone else has experienced this. And if is there something I can do.

Sounds like a thyroid issue. The symptoms you mention are consistent with low thyroid function (hypothyroidism). I have read that vegetable oils (except for coconut oil) lower thyroid function. These symptoms would not likely occur if your thyroid gland functioned at an optimum level. Blood tests could confirm this, or Google "basal temperature testing procedure". Broda Barnes developed this simple method of testing for low thyroid function. It is highly reliable, yet inexpensive.

Love this article. Just wanted to add my take to your wrap. When doing my wraps I use broccoli or a mixed bag of frozen veggies (ex broccoli, carrots, and cauliflower) and I skip the cheese and spread a thin layer of garlic hummus on the wrap. Its so good! I started sauteing with oil out of need. I have pollen allergy syndrome which makes me allergic to most raw veggies. I was scarred growing up with canned and boiled veggies which weren't appetizing in the least. Now that I'm a mommy I want my kids to eat right and I just started sauteing them and experimenting with flavors and so on. I was actually just Googling this subject to see if anyone else does this because I don't know anyonte else who does personally. I am happy to know there are actually more nutritional benefits this way!

I've just attended a wonderful address given by Dr Mary Flynn here in Geelong Australia. What an inspirational and informative speaker she is. In addition to our regular use of olive oils, vegetables cooked using EVOO will now be added to our daily diet. Thanks to Dr Mary. Liz Riordan

I love your book and your recipes. Thank you for all you do to inform people on the importance of using extra virgin olive oil in their diets. I hope one of these days, we as humans, will begin to turn the corner and get healthier by eating natural foods instead of fake processed foods.